1. Field of the Invention
The invention relates to ball and cone, variable-ratio, mechanical transmissions.
2. Description of The Prior Art
In the prior art, the ball and cone (ball friction) type of mechanical transmission is known. Its use provides a smoothly variable transmission ratio for applications where step-wise ratio variation is undesirable. Particular examples are disclosed in the patent literature of various industrial nations, and these prior art devices have one particular feature in common, namely a large interior angle of the cone concave surfaces in contact with the friction ball.
It has been assumed in the prior art, that a relatively large interior cone surface angle (small exterior angle) is advantageous for reducing operating friction and wear as a function of the level of power transmitted.
The following table lists the cone angles of some known friction transmissions.
______________________________________ Exterior Cone Angle ______________________________________ German Patent 1,176,422 12.degree. German Patent 1,102,516 54.degree. German Patent 864,021 8.degree.-15.degree. German Patent 720,240 34.degree. German Patent 721,825 35.degree. ______________________________________
The cone angle or exterior angle in the sense of the above table and in the arrangement of the invention is the angle which is designated .alpha. in FIG. 1 of the accompanying drawing, i.e., the angle between the conical surface and a line perpendicular to the input or output shaft, these shafts being substantially parallel to each other.
If a very small or very large exterior cone angle (.alpha.) is chosen (cf. table), the operation of the device will be insured, but optimum efficiency will not be achieved.
The manner in which the present invention provides optimization of operability, life and efficiency will be evident from the description hereinafter.